1. Field of the Invention
The present invention relates to a secondary battery using a negative electrode in which an alloy is used for a negative electrode active material thereof.
2. Description of the Related Art
In recent years, high-capacity fabrication of a lithium ion secondary battery which is a power supply has been desired along with high-performance and multifunction fabrication of a mobile communication apparatus.
However, a lithium ion secondary battery used at the present day uses lithium cobalt oxide as positive electrode active material and graphite as negative electrode active material, and the lithium secondary battery according to these materials is used based on a capacity which is already near the theoretical capacity, so that it has become in a situation that a still higher capacity fabrication thereof is extremely difficult.
For this reason, in recent years, investigation of a high capacity negative electrode which uses silicon (Si), tin (Sn) or the like as the negative electrode active material has been carried out actively. However, when these electrodes repeat charge and discharge, the current collection ability thereof decreases, because the active materials repeat expansion and contraction drastically and are smashed and atomized. Also, decomposition of the electrolyte is accelerated along with increase of surface area of the negative electrode in which deterioration of cycle characteristic is drastic.
Consequently, apart from a method in the past which coats slurry including granulous binder or the like, there has been reviewed a method for forming negative electrode active material for the negative electrode current collector by using vapor method, liquid phase method, sintering method, spraying method or the like (for example, see Patent Document 1, Patent Document 2 and Patent Document 3). According to this method, it is possible to repress atomization as compared with the coating type electrode in the past and at the same time, it is possible to integrate the negative electrode current collector and the negative electrode active material layer, so that electron conductivity in the negative electrode becomes extremely favorable and high-performance fabrication is expected in point of capacity and also in point of cycle life.
However, even in the negative electrode in which the current collector and the active material layer are integrated in this manner, peeling of the current collector and the active material layer arising from expansion or contraction of the active material layer occurs, so that it was difficult to obtain an adequate characteristic. Consequently, for example, there was proposed a method in which components of the negative electrode current collector are diffused in the negative electrode active material layer, adhesiveness of the negative electrode current collector and the negative electrode active material layer is heighten and at the same time, expansion and contraction in the diffusion region is repressed (for example, see Patent Document 4). Also, there was proposed a method in which impurity is added in the negative electrode active material layer and inclination structure is employed by changing the impurity concentration in the thickness direction (for example, see Patent Document 5).
[Patent Document 1] Japanese unexamined publication No. H8-50922
[Patent Document 2] Japanese Patent No. 2948205
[Patent Document 3] Japanese unexamined publication No. H11-135115
[Patent Document 4] Pamphlet of PCT unexamined publication No. WO01/029912
[Patent Document 5] Pamphlet of PCT unexamined publication No. WO01/031721